The taste system is a useful model for examining several fundamental aspects of sensory biology, including receptor cell replacement, cell commitment, and the interaction between nerve and their target receptor cells. Transcriptional regulation plays an important role in these processes. The focus of this proposal is to isolate and characterize trancription factors that are involved in regulating transcription in taste buds. The long range goal is to use the information obtained in these experiments to examine the mechanisms of taste cell differentiation. Specific AIM 1. Analyze the expression of the heleix-loop-helix transcription regulators REB and Id in taste buds. Two Id genes and tow novel REB splice variants will be isolated. The proportional expression of these splice variants and the Id genes will be compared in taste and non-taste tissues. Specific Aim 2. Analyze the expression of Id and REB genes during taste bud development and regeneration. Specific Aim 3. Isolate proteins expressed in taste buds that interact with REB. REB activates transcription after heterodimerizing with cell-specific HLH proteins, and therefore REB may dimerize with taste cell-specific HLH proteins to regulate taste cell differentiation. The two-hybrid system will be used to isolate proteins from taste tissue that dimerize with REB. Specific Aim 4. Analyze the activity of novel REB splice variants in vivo and in vitro. Differential expression of splice variants is one way in which class A HLH genes (such as REB) cna exert cell-specific influences. The dimerization and transactivation capabilities of the novel REB splice variants will be analyzed using in vivo and in assays.